Baghdad's Green Zone - officially the International Zone - is a heavily fortified area of closed-off streets in central Baghdad where most Iraqi government offices and the US embassy are located.

This area of about 10 square kilometres is supposed to be the most secure place in the country.

Its land-based perimeter is surrounded by concrete blast walls - designed to stop suicide bombers penetrating the nerve centres of official power. The River Tigris acts as a natural defensive barrier along its remaining circumference.

Iraq's parliament - in the old Islamic Conference centre built by Saddam Hussein - is an island of its own within the Green Zone, and to reach it visitors must negotiate concentric rings of armed checkpoints that start from the zone's outer borders.

There are about five vehicle entrances on the Green Zone perimeter - and three further pedestrian-only gates - where visitors will be stopped for the first time.

Politicians and diplomats have very different credentials to the workers that sweep the streets - and subsequent security checks inside the area will likely vary according to who you are.

Ordinary people undergo a full body search. Dogs sniff for explosives, luggage and equipment are opened. Electronic vehicle scanners screen large cars and lorries.

After these outer security measures, visitors face a number of similar checkpoints depending on which part of the zone they are heading to. Many of these are manned by US troops, but some by Iraqi soldiers or private security personnel.

We blame the security checks that we have in the parliament building, which we always complained and have concerns about

MP Layla Khafaji

There may be up to eight checks for those heading to the Parliamentary Zone.

Visitors to the parliament must be met at the building perimeter by their sponsor. They will then undergo further searches with airport-style scanners and dogs.

Military police can stop and search people en route in the Green Zone at any time.

The numerous armed posts - with their coils of razor wire and chain link fencing - have led to the area often being referred to as the "ultimate gated community".

But the suicide attack on the parliament building has shattered this image.

'Suicide belts' found

Security measures in the zone had supposedly been stepped up after a number of recent incidents.

The parliament blast was also a symbolic strike at Iraq's inner sanctum

Several weeks ago two discarded "suicide belts" were found in the zone.

In late March, Iraq's deputy prime minister was injured when a suicide bomber blew himself up near his home in the zone.

A day earlier, UN chief Ban Ki-moon was shaken after a mortar round landed in the Green Zone as he was holding a news conference.

The US military says that despite these breaches, security has been improving in parts of Baghdad.

Fareed Sabri, spokesman of the Iraqi Islamic Party in the UK, told the BBC: "Some of the MPs in Iraq, their body guards have been infiltrated by al-Qaeda and al-Qaeda operatives have really been monitoring a lot of what is going on inside the Iraqi parliament, and what is going on inside the Iraqi ministries.

"And I am sure some of the MPs have got people who are either affiliated to al-Qaeda... who have been able to smuggle bombs inside the Iraqi parliament.

"It's very difficult to check all those bodyguards - in Iraq there are at least 10,000 bodyguards for the politicians, one of the ministers has got about 750 bodyguards, so how can you check all the backgrounds of all those people?"

Layla Khafaji - an MP from the United Iraq Alliance - was in a nearby room when the bomb went off in the Iraqi parliament's cafe.

"We blame the security checks that we have in the parliament building, which we always complained and have concerns about," she said.

"We see some of the bodyguards for some of the parliamentarians enter with their weapons. Some of them - I heard - refused to get checked out at the checkpoints, in the front door or the back door.

"So this is a weakness in the security situation which makes these incidents happen."

There are also fears that the security problems will have wider repercussions.

Rajiv Chandrasekaran is author of a book on life in the Green Zone - Imperial Life in the Emerald City.

"The current Bush administration security plan for Baghdad, this troop surge, is based upon this notion that if you create pockets of security in Baghdad, political leaders will come together to make the necessary compromises to move forward on important pieces of legislation aimed at national reconciliation," Mr Chandrasekaran said.

"But if your parliament has been blown up, if legislators don't feel secure coming to work, it's hard to see how you can move forward with those very important political reconciliation initiatives."